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News Article

Partly logged forests still valuable for mammal conservation


 Thinning can increase animal numbers

Among conservationists, old-growth forests are generally viewed as the most valuable ecosystems, with logging seen as degrading the environment and reducing biodiversity compared with untouched forests. But a new study published in the journal Biological Conservation finds that not only are “degraded” forests, logged multiple times, still a valuable habitat, but logging can actually increase numbers of mammals present.

The research by Oliver Wearn of the Zoological Society of London and co-workers collected data from camera- and live-trapping in Borneo, and estimated the relative abundance of 57 terrestrial mammal species across a land use gradient which included old-growth tropical forest, logged forests, and oil palm plantations. They found that mean relative abundance actually increased (by 28%) from old-growth to logged forest, but declined substantially (by 47%) in oil palm plantations compared to forest.

The increase in mammal numbers after logging is not necessarily a good thing. From old-growth to logged forest, small mammals increased in their relative abundance proportionately much more than large mammals (169% compared to 13%), and previous work by the research group (Loveridge et al., 2016) found that selective logging in Borneo facilitated invasion by animals such as rats and feral dogs. But the logged forest did still act as a habitat to larger animals of high conservation value, including some of those that partly make their living in the treetops, like orangutans and clouded leopards. The caveat here is that this was at least partly due to hunting not being a problem in this particular study area. In other parts of the world, logging has made forests more accessible to hunters leading to mammal populations being decimated by hunting. There can also be a time delay in the response to logging, so long-term monitoring, and particular attention to species which are specialists to old-growth ecosystems, is needed to prove the habitat value of disturbed forest.

What the research did clearly demonstrate was that forests of all types were much better for wildlife than were oil palm plantations. From forest to oil palm, species of high conservation concern fared especially poorly (declining by 84%). Invasive species relative abundance consistently increased along the gradient of land-use intensity. The authors conclude that, in the absence of hunting, even the most intensively logged forests can conserve the abundance and functional effects of mammals. Recent pledges made by companies to support the protection of High Carbon Stock logged forest could therefore yield substantial conservation benefits. Within oil palm, the results support the view that so-called “wildlife-friendly” practices offer only a low potential for reducing biodiversity impacts.

Looking at other papers co-authored by Wearn and indexed on Forest Science, Cusack et al. (2015) compared detection of native and non-native murid species in logged and unlogged forests of northern Borneo. Within logged forest, detection probabilities of the three native species did not vary significantly with level of patch disturbance, whereas that of the invasive Rattus rattus increased markedly in more degraded sites. Wearn et al. (2013) found that intensively logged forest still had the full complement of wild cat species found in Borneo, including the bay cat Pardofelis badia, a poorly known Bornean endemic. Bernard et al. (2014) found more mammal species in continuously logged forest habitat in Borneo than in forest patches within an oil palm habitat matrix.

In other related work, Knop et al. (2004) found that orang-utan density did not differ significantly between primary forest and selectively logged forest, and that fruit availability was similar in the two forest types. Ancrenaz et al. (2010) suggest that orang-utan populations can be maintained in forests that have been lightly and sustainably logged, but that forests that are heavily logged or subjected to fast, successive coupes that follow conventional extraction methods, exhibit a decline in orang-utan numbers which will eventually result in localized extinction.

Other papers from Borneo can be found using the search Borneo AND de:(logging OR "disturbed forests" OR "ecological disturbance") AND (mammals OR wildlife). To find similar research from other parts of the world, replace Borneo in the search string with other locations, or with a habitat type such as “tropical forests”.

Journal reference 

Wearn, O. R., Rowcliffe, J. M., Carbone, C., Pfeifer, M., Bernard, H., & Ewers, R. M. (2017). Mammalian species abundance across a gradient of tropical land-use intensity: A hierarchical multi-species modelling approach. Biological Conservation212, 162-171. https://doi.org/10.1016/j.biocon.2017.05.007

Article details

  • Author(s)
  • David Simpson
  • Date
  • 22 August 2017
  • Subject(s)
  • Environment
  • Management